Philadelphia – a hub for US Airways – was among the hardest hit, with more than 145 arrivals and departures canceled as of 10:15 p.m. ET, according to FlightStats.

More than 80 flights had been canceled at New York LaGuardia while the total at Newark Liberty had neared 70 by 10 p.m. ET.

Other airports seeing a notable cancellations by early evening included Washington Reagan National (71), Atlanta (55), Charlotte (36) and Chicago O'Hare (30). All had been affected by strong storms for at least part of the day Monday.

And even where flights were operating, long delays had become a problem by late afternoon, according to the Federal Aviation Administration's flight delay map. The FAA was reporting average delays of more than 2 hours at both Philadelphia and and Baltimore/Washington as of 7:30 p.m. ET. Delays averaging between 50 and 2 hours were being reported at New York JFK, New York LaGuardia, Newark Liberty, Washington Dulles and Washington Reagan National.

Atlanta and Charlotte were seeing shorter delays, though the threat of storms remained across large areas of the East Coast into the evening.

US Airways spokesman Todd Lehmacher confirmed that the stormy weather and related air traffic control delays had made it a "tough go" for normal schedules at East Coast airports like Philadelphia, Washington Reagan National and Charlotte. He said US Airways and US Airways Express had canceled about 134 flights nationwide by late afternoon, though he noted that's just "a small percentage" of the airline's 3,100 daily flights.

To the west, wind and visibility was a problem earlier today at San Francisco International, where more than 70 flights had been canceled. Conditions had improved there by afternoon, though some sporadic delays had lingered into the late afternoon local time.